1. Field of the Invention
The present invention generally relates to a combustion engine utilizable as a drive source for a working machine such as a lawn mower and, more particularly, to the combustion engine, in which a cooling fan and a starter pulley are integrated together.
2. Description of the Prior Art
The drive source for a working machine such as a lawn mower is generally used in the form of a combustion engine of a vertical shaft type. This type of combustion engine includes a crankshaft so accommodated within a crankcase as to extend vertically. A lower end of the crankshaft protrudes downwardly and outwardly from the crankcase to serve as a drive output shaft. As an example of the mounting structure for a cooling fan and a starter pulley employed in the combustion engine of this kind, what is shown in FIG. 11 is currently available. See, for example, the Japanese Laid-open Utility Model Publication No. 5-24921 (the abstract on page 1 and the drawings).
Referring to FIG. 11, a vertically extending crankshaft 70 has an upper end 71, on which a flywheel 73 formed integrally with a cooling fan 72 is mounted, and a starter pulley 74 for receiving a starting force from a recoil starter (not shown) is fixed to the flywheel 73 by a set bolt 75. The cooling fan 72 is formed integrally with the flywheel 73 by casting a cast material such as cast iron by the use of a suitable casting such as a centrifugal casting or a die casting, thereby minimizing the number of component parts used.
It has, however, been found that when the flywheel 73 and the cooling fan 72 are formed integrally with each other by casting, it is necessary for blades of the cooling fan 72 to have a thickness as small as possible to increase the performance of the cooling fan 72 and, on the other hand, for the flywheel 73 to have an increased weight to increase the inertia force of rotation. To this end, the cooling fan 72 having the thin and complicated-shape blades will eventually be formed integrally with the bulky flywheel 73, making it difficult to accomplish the casting.